How might an asteroid form an impact feature
like a Carolina bay, so unlike a conventional round crater?

See Sandia Laboratory's recent model of what
could be the long sought mechnism for
Carolina Bay formation: mulitple
"Tunguska class" airbursts of smaller asteroids sending a pillars of hell onto
the ground below.

INCINERATION POSSIBLE - Fine points of the "fireball" that might be expected
from an asteroid exploding in Earth's atmosphere are indicated in a
supercomputer simulation devised by a team led by Sandia researcher Mark
Boslough. (Photo by Randy Montoya )

Movie Clips and Descriptions from the
Sandia lab webpage:
The following clips are available for viewing. Apple's Quicktime is
available for download from Apple's website
here.

A 62 thousand ton stationary asteroid explodes with an
energy of 5 megatons at 5 km above the surface. The movie
window is 15 km wide and about 8 km high. Bright colors of the
fireball indicate temperature, ranging from steam (dull red) to
rock vapor (white). Gray background indicates air density and
shows a spherical blast wave that reflects from the ground. The
fireball rises buoyantly and cools as it recedes, limiting the
thermal effects on the surface. This simulation shows what
happens when momentum is ignored to simplify the problem as
scientists have done in the past. The airburst is approximated
by a "point source" explosion similar to a nuclear detonation.
-- Sandia

This simulation shows what happens when momentum is not
ignored, an approach that is allowed with modern supercomputers
and codes. The same asteroid is now moving through the
atmosphere at a typical impact velocity (20 km/s). For
illustration purposes, extra energy is deposited into the
asteroid when it reaches 5 km, for a total of 5 megatons.
Momentum carries the hot fireball down to the surface, which
enhances heat and wind effects on the ground.

Movie 8Close-up of the previous simulation. The box
dimensions are 4 km wide and 3 km high. The colors indicate the
energy associated with vorticity, the swirling, tornado-like
eddies generated by the downward motion. High velocity winds
can be sustained at ground level by vortex flow.

Movie 7Tracking of 5 megaton asteriod that begins
exploding at 20 km above the surface, but carries its energy
down to about 8 km. Axes are labeled in cm, and colors indicate
velocity in cm/s.

3D simulation of a 15 megaton explosion that is initiated
18 km above the surface, for an asteroid entering at an angle of
35 degrees above the horizontal. Box dimensions are 40 km wide,
20 km high. Colors indicate speed. The hot fireball decends to
the surface and slides downrange at high velocities, subjecting
the landscape to blast-furnace condtions. This did not happen
at Tunguska.

Map view of blast zone from 3-D simulation of a 15 megaton
explosion. Axes are labeled in centimeters, and colors indicate
wind speed. Expanding oblong shape is the blast wave moving
along the surface, blowing down trees with wind speeds
decreasing from high hurricane force of 60 m/s (magenta) to
below 20 m/s (yellow). Blast-furnace conditions are sustained
downrange (left) of the origin where the fireball contacted the
surface. This did not happen at Tunguska, so the asteroid must
have been smaller (less energetic).

3D simulation of a 5 megaton explosion that is initiated
12 km above the surface, for an asteroid entering at an angle of
35 degrees above the horizontal. Box dimensions are 40 km wide,
20 km high. Colors indicate speed. The hot fireball does not
reach the surface, but descends to an altitude of 5 km before
buoyantly rising. At ground zero, the blast wave comes from
directly above, consistent with observations of standing trees
at the Tunguska epicenter.

Movie 6Map view of blast zone from 3-D simulation of a 5
megaton explosion. Axes are labeled in centimeters, and colors
indicate wind speed. Expanding oblong shape is the blast wave
moving along the surface, blowing down trees with wind speeds
decreasing from high hurricane force of 60 m/s (magenta) to
below 20 m/s (yellow). Because the fireball stops at high
altitude, there is no blast furnace zone near the epicenter and
trees remain standing as observed at Tunugska.